I do enjoy reading Krugman, and I understand his continued hammering on the Euro (note: NY Times article link), but it kind of seems like shouting at the wind. No matter how bad an idea the single currency was, and no matter how imperfectly it was implemented, unwinding it seems nearly unthinkable. There was a moment of opportunity to do so when interest rates were all over the map, but it has mostly passed (of course it is likely to come again), and it passed because no one in the Euro-zone wants to go back. I would rather hear ways to make the Euro function, than continued harping on why it was such a bad idea/implementation.
The US does [fairly] well with a single currency (yes, I know, we have a fiscal union as well) and our states have a fair amount of autonomy, so it seems like the Euro could be made to work without complete fiscal integration. e.g. Implement some baseline values--min wage, max retirement age, min retirement income, min unemployment benefits--that the various nation-states would be able to go above and beyond if they wished. All of this would be covered by a Euro-zone tax that would be a % of GDP, with the individual nations able to determine how to levy that tax on their citizens.